The present invention relates to a method and device for controlling the fuel quantity injected into an internal combustion engine.
The present invention may be used to advantage, though not exclusively, in direct-injection diesel engines with a common rail injection system, to which the following description refers purely by way of example.
As is known, in current internal combustion engines, the fuel quantity actually injected into each cylinder at each injection may differ, at times even considerably, from the nominal quantity calculated by the electronic central injection control unit to meet driver requirements, and on the basis of which injector energization time is currently determined.
The difference between the nominal fuel quantity to be injected and the quantity actually injected is caused by various factors, foremost of which are deviations in injector characteristics caused by process spread and eventual drift, and ageing of the injection system.
Differing nominal and injected fuel quantities are always undesirable, but particularly so in the case of last-generation injection systems implementing multiple-injection strategies, in which small quantities of fuel are injected close to the main injection to assist the main injection at the actual fuel combustion stage.
In the case of small fuel quantities, the error introduced sometimes results in no fuel being injected at all, thus defeating the object of multiple injection strategies, and so increasing the noise and exhaust gas emission levels of the engine.
It is an object of the present invention to provide a method and device for controlling the fuel quantity injected into an internal combustion engine, in particular a diesel engine equipped with a common rail injection system, designed to eliminate the aforementioned drawbacks.
According to the present invention, there is provided a control method for controlling the fuel quantity injected into an internal combustion engine comprising a number of injectors, each for injecting a given fuel quantity into a respective cylinder; for each injection inside a cylinder of said engine, said method comprising the step of determining a nominal energization time of the injector involved in said injection, as a function of injection pressure and the required nominal fuel quantity; and said method being characterized by comprising the steps of: determining a correction energization time as a function of injection pressure and the cylinder involved in the injection; determining, in the event the required nominal fuel quantity is below a predetermined threshold, a corrected energization time by correcting said nominal energization time as a function of said correction energization time; and exciting said injector for a time equal to said corrected energization time; said step of determining said correction energization time comprising the steps of: performing, in the presence of a predetermined series of operating conditions of said engine, a succession of energizations of said injector of gradually increasing energization times; determining a quantity related to the output torque of said engine in response to said succession of energizations; and calculating said correction energization time as a function of said quantity related to the output torque.
According to the present invention, there is also provided a control device for controlling the fuel quantity injected into an internal combustion engine comprising a number of injectors, each for injecting a given fuel quantity into a respective cylinder; said control device being characterized by comprising: energization means for determining a nominal energization time of said injector as a function of injection pressure and the nominal fuel quantity required by the user; correcting means for determining a correction energization time as a function of injection pressure and the cylinder involved in said injection; control means for determining, in the event the required nominal fuel quantity is below a predetermined threshold, a corrected energization time by correcting said nominal energization time as a function of said correction energization time; and drive means for exciting said injector for a time equal to said corrected energization time; said correcting means comprising: control means for performing, in the presence of a predetermined series of operating conditions of said engine, a succession of energizations of an injector with gradually increasing energization times; detecting means for determining a quantity related to the output torque of said engine in response to said succession of energizations; and processing means for calculating said correction energization time as a function of said quantity related to the output torque.